Hydrocarbon dehydrogenation with an attenuated superactive multimetallic catalytic composite for use therein

ABSTRACT

Dehydrogenatable hydrocarbons are dehydrogenated by contacting them, at hydrocarbon dehydrogenation conditions, with a novel attenuated superactive multimetallic catalytic composite comprising a combination of a catalytically effective amount of a pyrolyzed rhenium carbonyl component with a porous carrier material containing a uniform dispersion of catalytically effective amounts of a platinum group component maintained in the elemental metallic state, and of a tin component. An example of the attenuated superactive nonacidic multimetallic catalytic composite disclosed herein is a combination of a catalytically effective amount of a pyrolyzed rhenium carbonyl component with a porous carrier material containing a uniform dispersion of catalytically effective amounts of an alkali or alkaline earth component, a tin component, and of a platinum group component which is maintained in the elemental metallic state during the incorporation of the rhenium carbonyl component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of my prior, copendingapplication Ser. No. 68,278 filed Aug. 20, 1979 and issued Mar. 17, 1981as U.S. Pat. No. 4,256,566; which in turn is a continuation-in-part ofmy prior application Ser. No. 833,332 filed Sept. 14, 1977 and issuedAug. 21, 1979 as U.S. Pat. No. 4,165,276. All of the teachings of theseprior applications are specifically incorporated herein by reference.

The subject of the present invention is, broadly, an improved method fordehydrogenating dehydrogenatable hydrocarbon to produce a hydrocarbonproduct containing the same number of carbon atoms but fewer hydrogenatoms. In another aspect, the present invention involves a method ofdehydrogenating normal paraffin hydrocarbons containing 3 to 30 carbonatoms per molecule to the corresponding normal mono-olefin with minimumproduction of side products. In yet another aspect, the presentinvention relates to a novel attenuated superactive nonacidicmultimetallic catalytic composite comprising a combination of acatalytically effective amount of a pyrolyzed rhenium carbonyl componentwith a porous carrier material containing a uniform dispersion ofcatalytically effective amounts of an alkali or alkaline earthcomponent, a tin component, and a platinum group component which ismaintained in the elemental metallic state. This nonacidic composite hashighly beneficial characteristics of activity, selectivity, andstability when it is employed in the dehydrogenation of dehydrogenatablehydrocarbons such as aliphatic hydrocarbons, naphthene hydrocarbons, andalkylaromatic hydrocarbons.

The conception of the present invention followed from my search for anovel catalytic composite possessing a hydrogenation-dehydrogenationfunction, a controllable cracking function, and superior conversion,selectivity, and stability characteristics when employed in hydrocarbonconversion processes that have traditionally utilized dual-functioncatalytic composites. In my prior application Ser. No. 68,278, Idisclosed a significant finding with respect to a multimetalliccatalytic composite meeting these requirements. More specifically, Idetermined that a pyrolyzed rhenium carbonyl component can be utilized,under certain specified conditions, to beneficially interact with theplatinum group and tin components of a dual-function catalyst with aresulting marked improvement in the performance of such a catalyst. NowI have ascertained that a catalytic composite, comprising a combinationof catalytically effective amounts of a platinum group component, apyrolyzed rhenium carbonyl component and a tin component with a porouscarrier material can have superior activity, selectivity and stabilitycharacteristics when it is employed in a hydrocarbon dehydrogenationprocess if these components are uniformly dispersed in the porouscarrier material in the amounts specified hereinafter and if theoxidation state of the platinum group component is carefully controlledso that substantially all of this component is present in the elementalmetallic state during the incorporation of the rhenium carbonylcomponent. I have discerned, moreover, that a particularly preferredmulti-metallic catalytic composite of this type contains not only aplatinum group component, a tin component, and a pyrolyzed rheniumcarbonyl component, but also an alkali or alkaline earth component in anamount sufficient to ensure that the resulting catalyst is nonacidic.

The dehydrogenation of dehydrogenatable hydrocarbons is an importantcommercial process because of the great and expanding demand fordehydrogenated hydrocarbons for use in the manufacture of variouschemical products, such as detergents, plastics, synthetic rubbers,pharmaceutical products, high octane gasolines, perfumes, drying oils,ion-exchange resins, and various other products well known to thoseskilled in the art. One example of this demand is in the manufacture ofhigh octane gasoline by using C₃ and C₄ mono-olefins to alkylateisobutane. Another example of this demand is in the area ofdehydrogenation of normal paraffin hydrocarbons to produce normalmono-olefins having 3 to 30 carbon atoms per molecule. These normalmono-olefins can, in turn, be utilized in the synthesis of a vast numberof other chemical products. For example, derivatives of normalmono-olefins have become of substantial importance to the detergentindustry where they are utilized to alkylate an aromatic, such asbenzene, with subsequent transformation of the product arylalkane into awide variety of biodegradable detergents such as alkylaryl sulfonatetypes of detergents which are most widely used today for household,industrial, and commercial purposes. Still another large class ofdetergents produced from these normal mono-olefins are the oxyalkylatedphenol derivatives in which the alkylphenol base is prepared by thealkylation of phenyl with these normal mono-olefins. Still another typeof detergent produced from these normal mono-olefins are thebiodegradable alkylsulfonates formed by the direct sulfation of thenormal mono-olefins. Likewise, the olefin can be subjected to directsulfonation with sodium bisulfite to make biodegradable alkylsulfonates.As a further example, these mono-olefins can be hydrated to producealcohols which then, in turn, can be used to produce plasticizers and/orsynthetic lube oils.

Regarding the use of products made by the dehydrogenation ofalkylaromatic hydrocarbons, they find wide application in the petroleum,petrochemical, pharmaceutical, detergent, plastic, and the likeindustries. For example, ethylbenzene is dehydrogenated to producestyrene which is utilized in the manufacture of polystyrene plastics,styrene-butadiene rubber, and the like products. Isopropylbenzene isdehydrogenated to form alpha-methyl styrene which, in turn, isextensively used in polymer formation and in the manufacture of dryingoils, ion-exchange resins, and the like materials.

Responsive to this demand for these dehydrogenation products, the arthas developed a number of alternative methods to produce them incommercial quantities. One method that is widely utilized involves theselective dehydrogenation of a dehydrogenatable hydrocarbon bycontacting the hydrocarbon with a suitable catalyst at dehydrogenationconditions. As is the case with most catalytic procedures, the principalmeasure of effectiveness for this dehydrogenation method involves theability of the catalyst to perform its intended function with minimuminterference of side reactions for extended periods of time. Theanalytical terms used in the art to broadly measure how well aparticular catalyst performs its intended functions in a particularhydrocarbon conversion reaction are activity, selectivity, andstability, and for purposes of discussion here, these terms aregenerally defined for a given reactant as follows: (1) activity is ameasure of the catalyst's ability to convert the hydrocarbon reactantinto products at a specified severity level where severity level meansthe specific reaction conditions used--that is, the temperature,pressure, contact time, and presence of diluents such as H₂ ; (2)selectivity usually refers to the amount of desired product or productsobtained relative to the amount of the reactant charged or converted;(3) stability refers to the rate of change with time of the activity andselectivity parameters--obviously, the smaller rate implying the morestable catalyst. In a dehydrogenation process, more specifically,activity commonly refers to the amount of conversion that takes placefor a given dehydrogenatable hydrocarbon at a specified severity leveland is typically measured on the basis of disappearance of thedehydrogenatable hydrocarbon; selectivity is typically measured by theamount, calculated on a mole or weight percent of converteddehydrogenatable hydrocarbon basis, of the desired dehydrogenatedhydrocarbon obtained at the particular activity or severity level; andstability is typically equated to the rate of change with time ofactivity as measured by disappearance of the dehydrogenatablehydrocarbon and of selectivity as measured by the amount of desireddehydrogenated hydrocarbon produced. Accordingly, the major problemfacing workers in the hydrocarbon dehydrogenation art is the developmentof a more active and selective catalytic composite that has goodstability characteristics.

I have now found an attenuated superactive multimetallic catalyticcomposite which possesses improved activity, selectivity, and stabilitywhen it is employed in a process for the dehydrogenation ofdehydrogenatable hydrocarbons. In particular, I have determined that theuse of an attenuated superactive multimetallic catalyst, comprising acombination of catalytically effective amounts of a platinum groupcomponent, a pyrolyzed rhenium carbonyl component and a tin componentwith a porous refractory carrier material, can enable the performance ofa hydrocarbon dehydrogenation process to be substantially improved ifthe platinum group component is uniformly dispersed throughout thecarrier material prior to incorporation of the rhenium carbonylcomponent, if the oxidation state of the platinum group component ismaintained in the elemental metallic state prior to and during contactwith the rhenium carbonyl component and if high temperature treatmentsin the presence of oxygen and/or water of the reaction product of therhenium carbonyl with the carrier material containing the platinum groupcomponent is avoided. Moreover, particularly good results are obtainedwhen this composite is combined with an amount of an alkali or alkalineearth component sufficient to ensure that the resulting catalyst isnonacidic and utilized to produce dehydrogenated hydrocarbons containingthe same carbon structure as the reactant hydrocarbon but fewer hydrogenatoms. This nonacidic composite is particularly useful in thedehydrogenation of long chain normal paraffins to produce thecorresponding normal mon-olefin with minimization of side reactions suchas skeletal isomerization, aromatization, cracking and polyolefinformation. In sum, the present invention involves the significantfinding that a pyrolyzed rhenium carbonyl component can be utilizedunder the circumstances specified herein to beneficially interact withand promote a hydrocarbon dehydrogenation catalyst containing a platinumgroup metal and tin.

It is accordingly, one object of the present invention to provide anovel method for the dehydrogenation of dehydrogenatable hydrocarbonsutilizing an attenuated superactive multimetallic catalytic compositecomprising catalytically effective amounts of a platinum groupcomponent, a pyrolyzed rhenium carbonyl component, and a tin componentcombined with a porous carrier material. A second object is to provide anovel nonacidic catalytic composite having superior performancecharacteristics when utilized in a hydrocarbon dehydrogenation process.Another object is to provide an improved method for the dehydrogenationof normal paraffin hydrocarbons to produce normal mono-olefins, whichmethod minimizes undesirable side reactions such as cracking, skeletalisomerization, polyolefin formation, disproportionation andaromatization.

In brief summary, one embodiment of the present invention involves amethod for dehydrogenating a dehydrogenatable hydrocarbon whichcomprises contacting the hydrocarbon at hydrocarbon dehydrogenationconditions with an attenuated superactive multimetallic catalyticcomposite comprising a porous carrier material containing a uniformdispersion of catalytically effective and available amounts of aplatinum group component, a tin component and of a pyrolyzed rheniumcarbonyl component. Substantially all of the platinum group componentis, moreover, present in the composite in the elemental metallic stateduring the incorporation of the rhenium carbonyl component and thepyrolysis of the rhenium carbonyl component is performed after it hasbeen reacted with the porous carrier material containing the platinumgroup and tin components. Further, these components are preferablypresent in this composite in amounts, calculated on an elemental basis,sufficient to result in the composite containing about 0.01 to about 2wt. % platinum group metal, about 0.01 to about 5 wt. % rhenium derivedfrom the rhenium carbonyl component, and about 0.005 to about 5 wt. %tin, and this composite is preferably maintained in a substantiallyhalogen-free state during use in the dehydrogenation method.

A second embodiment relates to the dehydrogenation method described inthe first embodiment wherein the dehydrogenatable hydrocarbon is analiphatic compound containing 2 to 30 carbon atoms per molecule.

A third embodiment comprehends an attenuated superactive nonacidiccatalytic composite comprising a porous carrier material havinguniformly dispersed therein catalytically effective and availableamounts of a platinum group component, a pyrolyzed rhenium carbonylcomponent, a tin component, and an alkali or alkaline earth component.These components are preferably present in amounts sufficient to resultin the catalytic composite containing, on an elemental basis, about 0.01to about 2 wt. % platinum group metal, about 0.005 to about 5 wt. % tin,about 0.1 to about 5 wt. % alkali metal or alkaline earth metal andabout 0.01 to about 5 wt. % rhenium, derived from the rhenium carbonylcomponent. In addition, substantially all of the platinum groupcomponent is present in the elemental metallic state duringincorporation of the rhenium carbonyl component, the pyrolysis of therhenium carbonyl component occurs after combustion thereof with theporous carrier material containing the platinum group and tin componentsand substantially all of the alkali or alkaline earth component ispresent in an oxidation state above that of the elemental metal.

Another embodiment pertains to a method for dehydrogenating adehydrogenatable hydrocarbon which comprises contacting the hydrocarbonwith the nonacidic catalytic composite described in the third embodimentat dehydrogenation conditions.

Other objects and embodiments of the present invention involve specificdetails regarding essential and preferred catalytic ingredients,preferred amounts of ingredients, suitable methods of multimetalliccomposite preparation, suitable dehydrogenatable hydrocarbons, operatingconditions for use in the dehydrogenation process, and the likeparticulars. These are hereinafter given in the following detaileddiscussion of each of these facets of the present invention. It is to beunderstood that (1) the term "nonacidic" means that the catalystproduces less than 10% conversion to 1-butene to isobutylene when testedat dehydrogenation conditions and, preferably, less than 1%; (2) theexpression "uniformly dispersed throughout the carrier material" isintended to mean that the amount of the subject component, expressed ona weight percent basis, is approximately the same in any reasonablydivisible portion of the carrier material as it is in gross; and (3) theterm "substantially hologen-free" means that the total amount of halogenpresent in the catalytic composite in any form is less than about 0.2wt. %, calculated on an elemental basis.

Regarding the dehydrogenatable hydrocarbon that is subjected to themethod of the present invention, it can, in general, be an organiccompound having 2 to 30 carbon atoms per molecule and containing atleast one pair of adjacent carbon atoms having hydrogen attachedthereto. That is, it is intended to include within the scope of thepresent invention, the dehydrogenation of any organic compound capableof being dehydrogenated to produce products containing the same numberof carbon atoms but fewer hydrogen atoms, and capable of being vaporizedat the dehydrogenation temperatures used herein. More particularly,suitable dehydrogenatable hydrocarbons are: aliphatic hydrocarbonscontaining 2 to 30 carbon atoms per molecule, alkylaromatic hydrocarbonswhere the alkyl group contains 2 to 6 carbon atoms, and naphthenes oralkyl-substituted naphthenes. Specific examples of suitabledehydrogenatable hydrocarbons are: (1) alkanes such as ethane, propane,n-butane, isobutane, n-pentane, isopentane, n-hexane, 2-methylpentane,3-methylpentane, 2,2-dimethylbutane, n-heptane, 2-methylhexane,2,2,3-trimethylbutane, and the like compounds; (2) naphthenes such ascyclopentane, cyclohexane, methylcyclopentane, ethylcyclopentane,n-propylcyclopentane, 1,3-dimethylcyclohexane, and the like compounds;and (3) alkylaromatics such as ethylbenzene, n-butylbenzene,1,3,5-triethylbenzene, isopropylbenzene, isobutylbenzene,ethylnaphthalene, and the like compounds.

In a preferred embodiment, the dehydrogenatable hydrocarbon is a normalparaffin hydrocarbon having about 3 to 30 carbon atoms per molecule. Forexample, normal paraffin hydrocarbons containing about 10 to 18 carbonatoms per molecule are dehydrogenated by the subject method to producethe corresponding normal mono-olefin which can, in turn, be alkylatedwith benzene and sulfonated to make alkylbenzene sulfonate detergentshaving superior biodegradability. Likewise, n-alkanes having 10 to 18carbon atoms per molecule can be dehydrogenated to the correspondingnormal mono-olefin which, in turn, can be sulfonated or sulfated to makeexcellent detergents. Similarly, n-alkanes having 6 to 10 carbon atomscan be dehydrogenated to form the corresponding mono-olefin which can,in turn, be hydrated to produce valuable alcohols. Preferred feedstreams for the manufacture of detergent intermediates contain a mixtureof 4 or 5 adjacent normal paraffin homologues such as C₁₀ to C₁₃, C₁₁ toC₁₄, C₁₁ to C₁₅ and the like mixtures. In an especially preferredembodiment, the charge stock to the present method is substantially purepropane.

The attenuated superactive multimetallic catalyst used in the presentinvention comprises a porous carrier material or support having combinedtherewith a uniform dispersion of catalytically effective amounts of aplatinum group component, a pyrolyzed rhenium carbonyl component, a tincomponent, and, in the preferred case, an alkali or alkaline earthcomponent.

Considering first the porous carrier material utilized in the presentinvention, it is preferred that the material be a porous, adsorptive,high surface area support having a surface area of about 25 to about 500m² /g. The porous carrier material should be relatively refractory tothe conditions utilized in the hydrocarbon dehydrogenation process, andit is intended to include within the scope of the present inventioncarrier materials which have traditionally been utilized indual-function hydrocarbon conversion catalysts such as: (1) activatedcarbon, coke, or charcoal; (2) silica or silica gel, silicon carbide,clays, and silicates including those synthetically prepared andnaturally occurring, which may or may not be acid treated, for example,attapulgus clay, china clay, diatomaceous earth, fuller's earth, kaolin,kieselguhr, etc.; (3) ceramics, porcelain, crushed firebrick, bauxite;(4) refractory inorganic oxides such as alumina, titanium dioxide,zirconium dioxide, chromium oxide, beryllium oxide, vanadium oxide,cesium oxide, hafnium oxide, zinc oxide, magnesia, boria, thoria,silica-alumina, silica-magnesia, chromia-alumina, alumina-boria,silica-zirconia, etc.; (5) crystalline zeolitic aluminosilicates such asnaturally occurring or synthetically prepared mordenite and/orfaujasite, either in the hydrogen form or in a form which has beentreated with multivalent cations; (6) spinels such as MgAl₂ O₄, FeAl₂O₄, ZnAl₂ O₄, CaAl₂ O₄, and other like compounds having the formulaMO-Al₂ O₃ where M is a metal having a valence of 2; and (7) combinationsof elements from one or more of these groups. The preferred porouscarrier materials for use in the present invention are refractoryinorganic oxides, with best results obtained with an alumina carriermaterial. Suitable alumina materials are the crystalline aluminas knownas gamma-, eta-, and theta-alumina, with gamma- or eta-alumina givingbest results. In addition, in some embodiments the alumina carriermaterial may contain minor proportions of other well-known refractoryinorganic oxides such as silica, zirconia, magnesia, etc.; however, thepreferred support is substantially pure gamma- or eta-alumina. Preferredcarrier materials have an apparent bulk density of about 0.2 to about0.8 g/cc and surface area characteristics such that the average porediameter is about 20 to 300 Angstroms (B.E.T.), the pore volume is about0.1 to about 1 cc/g (B.E.T.) and the surface area is about 100 to about500 m² /g (B.E.T.). In general, best results are typically obtained witha substantially halogen-free gamma-alumina carrier material which isused in the form of spherical particles having a relatively smalldiameter (i.e. typically about 1/16 inch), an apparent bulk density ofabout 0.2 to about 0.8 g/cc, a pore volume of about 0.3 to about 0.8cc/g (B.E.T.), and a surface area of about 125 to about 250 m² /g(B.E.T.).

The preferred alumina carrier material may be prepared in any suitablemanner and may be synthetically prepared or naturally occurring.Whatever type of alumina is employed, it may be activated prior to useby one or more treatments including drying, calcination, steaming, etc.,and it may be in a form known as activated alumina, activated alumina ofcommerce, porous alumina, alumina gel, etc. For example, the aluminacarrier may be prepared by adding a suitable alkaline reagent, such asammonium hydroxide, to a salt of aluminum such as aluminum chloride,aluminum nitrate, etc., in an amount to form an aluminum hydroxide gelwhich upon drying and calcining is converted to alumina. The aluminacarrier may be formed in any desired shape such as spheres, pills,cakes, extrudates, powders, granules, tablets, etc., and utilized in anydesired size. For the purpose of the present invention a particularlypreferred form of alumina is the sphere, and alumina spheres may becontinuously manufactured by the well-known oil drop method whichcomprises: forming an alumina hydrosol by any of the techniques taughtin the art and preferably by reacting aluminum metal with hydrochloricacid, combining the resultant hydrosol with a suitable gelling agent anddropping the resultant mixture into an oil bath maintained at elevatedtemperatures. The droplets of the mixture remain in the oil bath untilthey set and form hydrogel spheres. The spheres are then continuouslywithdrawn from the oil bath and typically subjected to specific agingtreatments in oil and an ammoniacal solution to further improve theirphysical characteristics. The resulting aged and gelled particles arethen washed and dried at a relatively low temperature of about 300° F.to about 400° F. and subjected to a calcination procedure at atemperature of about 850° F. to about 1300° F. for a period of about 1to about 20 hours. It is a good practice to subject the calcinedparticles to a high temperature treatment with steam in order to removeundesired acidic components such as residual chlorine and therebyprepare the preferred substantially halogen-free carrier material. Thispreparation procedure effects conversion of the alumina hydrogel to thecorresponding crystalline gamma-alumina. See the teachings of U.S. Pat.No. 2,620,314 for additional details.

Another particularly preferred alumina carrier material is synthesizedfrom a unique crystalline alumina powder which has been characterized inU.S. Pat. Nos. 3,852,190 and 4,012,313 as a by-product from a Zieglerhigher alcohol synthesis reaction as described in Zeigler's U.S. Pat.No. 2,892,858. For purposes of simplification, the name "Ziegleralumina" is used herein to identify this material. It is presentlyavailable from the Conoco Chemical Division of Continental Oil Companyunder the trademark Catapal. This material is an extremely high purityalpha-alumina monohydrate (boehmite) which after calcination at a hightemperature has been shown to yield a high purity gamma-alumina. It iscommercially available in three forms: (1) Catapal SB--a spray driedpowder having a typical surface area of 250 m² /g; (2) Catapal NG--arotary kiln dried alumina having a typical surface area of 180 m² /g;and (3) Dispal M--a finely divided dispersable product having a typicalsurface area of about 185 m² /g. For purposes of the present invention,the preferred starting material is the spray dried powder, Catapal SB.This alpha-alumina monohydrate powder may be formed into a suitablecatalyst material according to any of the techniques known to thoseskilled in the catalyst carrier material forming art. Spherical carriermaterial particles can be formed, for example, from this Ziegler aluminaby: (1) converting the alpha-alumina monohydrate powder into an aluminasol by reaction with a suitable peptizing acid and water and thereafterdropping a mixture of the resulting sol and a gelling agent into an oilbath to form spherical particles of an alumina gel which are easilyconverted to a gamma-alumina carrier material by known methods; (2)forming an extrudate from the powder by established methods andthereafter rolling the extrudate particles on a spinning disc untilspherical particles are formed which can then be dried and calcined toform the desired particles of spherical carrier material; and (3)wetting the powder with a suitable peptizing agent and thereafterrolling particles of the powder into spherical masses of the desiredsize in much the same way that children have been known to make parts ofsnowmen by rolling snowballs down hills covered with wet snow. Thealumina powder can also be formed in any other desired shape or type ofcarrier material known to those skilled in the art such as rods, pills,pellets, tablets, granules, extrudates and the like forms by methodswell-known to the practitioners of the catalyst carrier material formingart. The preferred type of carrier material for the present invention isa cylindrical extradate having a diameter of about 1/32" to about 1/8"(especially about 1/16") and a length to diameter (L/D) ratio of about1:1 to about 5:1, with a L/D ratio of about 2:1 being especiallypreferred. The especially preferred extrudate form of the carriermaterial is preferably prepared by mixing the alumina powder with waterand a suitable peptizing agent such as nitric acid, acetic acid,aluminum nitrate and the like material until an extrudable dough isformed. The amount of water added to form the dough is typicallysufficient to give a loss on ignition (LOI) at 500° C. of about 45 to 65wt. %, with a value of about 55 wt. % being especially preferred. On theother hand, the acid addition rate is generally sufficient to provideabout 2 to 7 wt. % of the volatile free alumina powder used in the mix,with a value of about 3 to 4% being especially preferred. The resultingdough is then extruded through a suitably sized die to form extrudateparticles. It is to be noted that it is within the scope of the presentinvention to treat the resulting dough with an aqueous alkaline reagentsuch as an aqueous solution of ammonium hydroxide in accordance with theteachings of U.S. Pat. No. 3,661,805. This treatment may be performedeither before or after extrusion, with the former being preferred. Theseparticles are then dried at a temperature of about 500° to 800° F. for aperiod of about 0.1 to about 5 hours and thereafter calcined at atemperature of about 900° F. to about 1500° F. for a period of about 0.5to about 5 hours to form the preferred extrudate particles of theZiegler alumina carrier material. In addition, in some embodiments ofthe present invention the Ziegler alumina carrier material may containminor proportions of other well-known refractory inorganic oxides suchas silica, titanium dioxide, zirconium dioxide, chromium oxide,beryllium oxide, vanadium oxide, cesium oxide, hafnium oxide, zincoxide, iron oxide, cobalt oxide, magnesia, boria, thoria, and the likematerials which can be blended into the extrudable dough prior to theextrusion of same. In the same manner crystalline zeoliticaluminosilicates such as naturally occurring or synthetically preparedmordenite and/or faujasite, either in the hydrogen form or in a formwhich has been treated with a multivalent cation, such as a rare earth,can be incorporated into this carrier material by blending finelydivided particles of same into the extrudable dough prior to extrusionof same. A preferred carrier material of this type is a substantiallyhalogen-free and substantially pure Ziegler alumina having an apparentbulk density (ABD) of about 0.4 to 1 g/cc (especially an ABD of about0.5 to about 0.85 g/cc), a surface area (B.E.T.) of about 150 to about280 m² /g (preferably about 185 to about 235 m² /g) and a pore volume(B.E.T.) of about 0.3 to about 0.8 cc/g.

A first essential ingredient of the subject catalyst is the platinumgroup component. That is, it is intended to cover the use of platinum,iridium, osmium, ruthenium, rhodium, palladium, or mixtures thereof as afirst component of the superactive catalytic composite. It is anessential feature of the present invention that substantially all ofthis platinum group component is uniformly dispersed throughout theporous carrier material in the elemental metallic state prior to theincorporation of the rhenium carbonyl ingredient. Generally, the amountof this component present in the form of catalytic composites is smalland typically will comprise about 0.01 to about 2 wt. % of finalcatalytic composite, calculated on an elemental basis. Excellent resultsare obtained when the catalyst contains about 0.05 to about 1 wt. % ofplatinum, iridium, rhodium or palladium metal. Particularly preferredmixtures of these platinum group metals preferred for use in thecomposite of the present invention are: (1) platinum and iridium and (2)platinum and rhodium.

This platinum group component may be incorporated in the porous carriermaterial in any suitable manner known to result in a relatively uniformdistribution of this component in the carrier material such ascoprecipitation or cogelation, ion-exchange or impregnation. Thepreferred method of preparing the catalyst involves the utilization of asoluble, decomposable compound of platinum group metal to impregnate thecarrier material in a relatively uniform manner. For example, thiscomponent may be added to the support by commingling the latter with anaqueous solution of chloroplatinic or chloroiridic or chloropalladicacid. Other water-soluble compounds or complexes of platinum groupmetals may be employed in impregnation solutions and include ammoniumchloroplatinate, bromoplatinic acid, platinum trichloride, platinumtetrachloride hydrate, platinum dichlorocarbonyl dichloride,dinitrodiaminoplatinum, sodium tetranitroplatinate (II), palladiumchloride, palladium nitrate, palladium sulfate, diamminepalladium (II)hydroxide, tetramminepalladium (II) chloride, hexamminerhodium chloride,rhodium carbonylchloride, rhodium trichloride hydrate, rhodium nitrate,sodium hexachlororhodate (III), sodium hexanitrorhodate (III), iridiumtribromide, iridium dichloride, iridium tetrachloride, sodiumhexanitroiridate (III), potassium or sodium chloroiridate, potassiumrhodium oxalate, etc. The utilization of a platinum, iridium, rhodium,or palladium chloride compound, such as chloroplatinic, chloroiridic, orchloropalladic acid or rhodium trichloride hydrate, is ordinarilypreferred. Nitric acid or the like acid is also generally added to theimpregnation solution in order to further facilitate the uniformdistribution of the metallic components throughout the carrier material.In addition, it is generally preferred to impregnate the carriermaterial after it has been calcined in order to minimize the risk ofwashing away the valuable platinum group component.

A second essential constituent of the multimetallic catalyst of thepresent invention is a tin component. This component may in general bepresent in the instant catalytic composite in any catalyticallyavailable form such as the elemental metal, a compound like the oxide,hydroxide, halide, oxyhalide, aluminate, or in chemical combination withone or more of the other ingredients of the catalyst. Although it is notintended to restrict the present invention by this explanation, it isbelieved that best results are obtained when the tin component ispresent in the composite in a form wherein substantially all of the tinmoiety is in an oxidation state above that of the elemental metal suchas in the form of tin oxide or tin halide or tin oxyhalide or in amixture thereof and the subsequently described oxidation and reductionsteps that are preferably used in the preparation of the instantcatalytic composite are specifically designed to achieve this end. Theterm "tin oxyhalide" as used herein refers to a coordinated complex oftin, oxygen, and halogen which are not necessarily present in the samerelationship for all cases covered herein. This tin component can beused in any amount which is catalytically effective, with good resultsobtained, on an elemental basis, with about 0.005 to about 5 wt. % tinin the catalyst. Best results are ordinarily achieved with about 0.01 toabout 1 wt. % tin, calculated on an elemental basis. The preferredatomic ratio of tin to platinum group metal for this catalyst is about0.1:1 to about 13:1.

This tin component may be incorporated in the catalytic composite in anysuitable manner known to the art to result in a relatively uniformdispersion of the tin moiety in the carrier material, such as bycoprecipitation or cogellation or coextrusion with the porous carriermaterial, ion exchange with the gelled carrier material, or impregnationof the porous carrier material either after, before, or during theperiod when it is dried and calcined. It is to be noted that it isintended to include within the scope of the present invention allconvention methods for incorporating and simultaneously uniformlydistributing a metallic component in a catalytic composite and theparticular method of incorporation used is not deemed to be an essentialfeature of the present invention. One particularly preferred method ofincorporating the tin component into the catalytic composite involvescogelling or coprecipitating the tin component in the form of thecorresponding hydrous oxide during the preparation of the preferredcarrier material, alumina. This method typically involves the additionof a suitable sol-soluble or sol-dispersible tin compound such asstannic or stannous chloride, tin acetate, and the like to the aluminahydrosol, thoroughly mixing the resulting tin-containing hydrosol inorder to uniformly disperse the tin moiety throughout the sol and thencombining the tin-containing hydrosol with a suitable gelling agent anddropping the resulting mixture into an oil bath, etc., as explained indetail hereinbefore. Alternatively, the tin compound can be added to thegelling agent. After drying and calcining the resulting gelled carriermaterial in air, there is obtained an intimate combination of aluminaand tin oxide and/or oxyhalide. A second preferred method ofincorporating the tin component into the catalytic composite involvesutilization of a soluble, decomposable compound of tin to impregnate theporous carrier material. In general, the solvent used in thisimpregnation step is selected on the basis of the capability to dissolvethe desired tin compound and to hold it in solution until it is evenlydistributed throughout the carrier material without adversely affectingthe carrier material or the other ingredients of the catalyst--forexample, a suitable alcohol, ether, acid and the like solvents. Thesolvent is preferably an aqueous, acidic solution. Thus, the tincomponent may be added to the carrier material by commingling the laterwith an aqueous acidic solution of a suitable tin salt, complex, orcompound such as stannic acetate, stannous or stannic bromide, stannousor stannic chloride, stannic chloride pentahydrate, stannic chloridediamine, stannic trichloride bromide, stannic chromate, stannous orstannic fluoride, stannic tartrate, dimethyltin dibromide, dimethyltindichloride, ethylpropyltin dichloride, triethyltin hydroxide,trimethyltin chloride, and the like compounds. A particularly preferredimpregnation solution comprises an acidic aqueous solution of stannic orstannous chloride. Suitable acids for use in the impregnation solutionare: inorganic acids such as hydrochloric acid, nitric acid, and thelike, and strongly acidic organic acids such as oxalic acid, malonicacid, citric acid, and the like. In general, the tin component can beimpregnated either prior to, simultaneously with, or after the platinumgroup component is added to the the carrier material. However, excellentresults are obtained when the tin component is incorporated into thecarrier material during its preparation and thereafter the platinumgroup component is added in a subsequent impregnation step after thetin-containing carrier material is calcined. A third preferred method ofadding the tin component is to select a rhenium-carbonyl complex thatalso contains a tin ligand in the subsequently describedrhenium-carbonyl incorporation step, thereby adding the tin componentsimultaneously with the rhenium-carbonyl component.

A highly preferred optional ingredient of the catalyst used in thepresent invention is an alkali or alkaline earth component. Morespecifically, this component is selected from the group consisting ofthe compounds of the alkali metals--cesium, rubidium, potassium, sodium,and lithium--and of the alkaline earth metals--calcium, strontium,barium, and magnesium. This component exists within the catalyticcomposite in an oxidation state above that of the elemental metal as arelatively stable compound such as the oxide or hydroxide, or incombination with one or more of the other components of the composite,or in combination with the carrier material such as, for example, in theform of an alkali or alkaline earth metal aluminate. Since, as isexplained hereinafter, the composite containing the alkali or alkalineearth component is always calcined or oxidized in an air atmospherebefore use in the dehydrogenation of hydrocarbons, the most likely statethis component exists in during use in the dehydrogenation reaction isthe corresponding metalic oxide such as lithium oxide, potassium oxide,sodium oxide, and the like. Regardless of what precise form in which itexists in the composite, the amount of this component utilized ispreferably selected to provide a nonacidic composite containing about0.1 to about 5 wt. % of the alkali metal or alkaline earth metal, and,more preferably, about 0.25 to about 3.5 wt. %. Best results areobtained when this component is a compound of lithium or potassium. Thefunction of this component is to neutralize any of the acidic materialsuch as halogen which may have been used in the preparation of thepresent catalyst so that the final catalyst is nonacidic.

The alkali or alkaline earth component may be combined with the porouscarrier material in any manner known to those skilled in the art toresult in a relatively uniform dispersion of this component throughoutthe carrier material with consequential neutralization of any acidicsites which may be present therein. Typically good results are obtainedwhen it is combined by impregnation, coprecipitation, ion-exchange, andthe like procedures. The preferred procedure, however, involvesimpregnation of the carrier material either before, during or after itis calcined, or before, during or after the other metallic ingredientsare added to the carrier material. Best results are ordinarily obtainedwhen this component is added to the carrier material simultaneously withor after the platinum group component and tin component, and before therhenium carbonyl component because the alkali metal or alkaline earthmetal component acts to neutralize the acidic materials used in thepreferred impregnation procedure for the platinum group and tincomponents. In fact, it is preferred to add the platinum group, tin andalkali or alkaline earth components to the carrier material, oxidize theresulting composite in a wet air stream at a high temperature (i.e.typically about 600° to 1000° F.), then treat the resulting oxidizedcomposite with steam or a mixture of air and steam at a relatively hightemperature of about 600° to about 1050° F. in order to remove at leasta portion of any residual acidity and thereafter add the rheniumcarbonyl component. Typically, the impregnation of the carrier materialwith this component is performed by contacting the carrier material witha solution of a suitable decomposable compound or salt of the desiredalkali or alkaline earth metal. Hence, suitable compounds include thealkali or alkaline earth metal halides, nitrates, acetates, carbonates,phosphates, and the like compounds. For example, excellent results areobtained by impregnating the carrier material with an aqueous solutionof chloroplatinic acid, lithium nitrate or potassium nitrate and nitricacid. Ordinarily, the amount of alkali or alkaline earth component isselected to produce a composite having an atomic ratio of alkali metalor alkaline earth metal to platinum group metal of about 5:1 to about100:1 or more, with the preferred range being about 10:1 to about 75:1.

After the platinum group component, tin (when the tin component is addedprior to the rhenium carbonyl incorporation step) component and optionalalkali or alkaline earth component are combined with the porous carriermaterial, the resulting metals-containing carrier material willgenerally be dried at a temperature of about 200° F. to about 600° F.for a period of typically about 1 to about 24 hours or more andthereafter oxidized at a temperature of about 600° F. to about 1100° F.in an air or oxygen atmosphere for a period of about 0.5 to about 10 ormore hours effective to convert substantially all of the platinum group,tin and alkali or alkaline earth components to the corresponding oxideforms. When acidic materials are used in incorporating these metalliccomponents, best results are ordinarily achieved when the resultingoxidized composite is subjected to a high temperature treatment withsteam or with a mixture of steam and a diluent gas such as air ornitrogen either during or after this oxidation step in order to removeas much as possible of the undesired acidic components such as halogenand thereby prepare a substantially halogen-free, metals-containingoxidized carrier material. It is to be noted that it is essential thatconditions used in this acidic component stripping step be verycarefully chosen to avoid any possibility of sintering or agglomeratingthe platinum group component.

A critical feature of the present invention involves subjecting theresulting oxidized, platinum group metal--and tin (when the tincomponent is added prior to the rhenium carbonyl incorporationstep)--containing, and typically alkali or alkline earthmetal-containing carrier material to a substantially water-freereduction step before the incorporation of the rhenium component bymeans of the rhenium carbonyl reagent. The importance of this reductionstep comes from my observation that when an attempt is made to preparethe instant catalytic composite without first reducing the platinumgroup component, no significant improvement in the platinum-rhenium-tincatalyst system is obtained; put another way, it is my finding that itis essential for the platinum group component to be well dispersed inthe porous carrier material in the elemental metallic state prior toincorporation of the rhenium component by the unique procedure of thepresent invention in order for synergistic interaction of the rheniumcarbonyl with the dispersed platinum group metal to occur according tothe theories that I have previously explained in my prior applicationSer. No. 68,278. Accordingly, this reduction step is designed to reducesubstantially all of the platinum group component to the elementalmetallic state and to assure a relatively uniform and finely divideddispersion of this metallic component throughout the porous carriermaterial. Preferably, a substantially pure and dry hydrogen-containingstream (by use of the word "dry" I mean that it contains less than 20vol. ppm. water and preferably less than 5 vol. ppm. water) is used asthe reducing agent in this step. The reducing agent is contacted withthe oxidized, platinum group metal- and tin-containing carrier materialat conditions including a reduction temperature of about 450° F. toabout 1200° F. for a period of about 0.5 to about 10 or more hoursselected to reduce substantially all of the platinum group component tothe elemental metallic state. Once this condition of finely divideddispersed platinum group metal in the porous carrier material isachieved, it is important that environments and/or conditions that coulddisturb or change this condition be avoided; specifically, I much preferto maintain the freshly reduced carrier material containing the platinumgroup metal under a blanket of inert gas to avoid any possibility ofcontamination of same either by water or by oxygen.

A third essential ingredient of the present attenuated superactivecatalytic composite is a rhenium component which I have chosen tocharacterize as a pyrolyzed rhenium carbonyl component in order toemphasize that the rhenium moiety of interest in my invention is therhenium produced by decomposing a rhenium carbonyl in the presence of afinely divided dispersion of a platinum group metal and in the absenceof materials such as oxygen or water which could interfere with thedesired interaction of the rhenium carbonyl component with the platinumgroup metal component. In view of the fact that all of the rheniumcontained in a rhenium carbonyl compound is present in the elementalmetallic state, an essential requirement of my invention is that theresulting reaction product of the rhenium carbonyl compound or complexwith the platinum group metal--and tin (when the tin component is addedprior to the rhenium carbonyl incorporation step)--loaded carriermaterial is not subjected to conditions which could in any way interferewith the maintenance of the rhenium moiety in the elemental metallicstate; consequently, avoidance of any conditions which would tend tocause the oxidation of any portion of the rhenium ingredient or of theplatinum group ingredient is a requirement for full realization of thesynergistic interaction enabled by the present invention. This rheniumcomponent may be utilized in the resulting composite in any amount thatis catalytically effective with the preferred amount typicallycorresponding to about 0.01 to about 5 wt. % thereof, calculated on anelemental rhenium basis. Best results are ordinarily obtained with about0.05 to about 1 wt. % rhenium. The traditional rule for rhenium-platinumcatalyst systems that best results are achieved when the amount of therhenium component is set as a function of the amount of the platinumgroup component also holds for my composition; specifically, I find bestresults are obtained with a rhenium to platinum group metal atomic ratioof about 0.1:1 to about 10:1, with an especially useful range comprisingabout 0.2:1 to about 5:1 and with superior results achieved at an atomicratio of rhenium to platinum group metal of about 1:1.

The rhenium carbonyl ingredient may be reacted with the reduced platinumgroup metal--and tin (when the tin component is added prior to therhenium carbonyl incorporation step)--containing porous carrier materialin any suitable manner known to those skilled in the catalystformulation art which results in relatively good contact between therhenium carbonyl complex and the platinum group component contained inthe porous carrier material. One acceptable procedure for incorporatingthe rhenium carbonyl compound into the composite involves sublimatingthe rhenium carbonyl complex under conditions which enable it to passinto the vapor phase without being decomposed and thereafter contactingthe resulting rhenium carbonyl sublimate with the platinum groupmetal--and tin--containing porous carrier material under conditionsdesigned to achieve intimate contact of the carbonyl reagent with theplatinum group metal dispersed on the carrier material. Typically, thisprocedure is performed under vacuum at a temperature of about 70° toabout 250° F. for a period of time sufficient to react the desiredamount of rhenium carbonyl complex with the carrier material. In somecases an inert carrier gas such as nitrogen can be admixed with therhenium carbonyl sublimate in order to facilitate the intimatecontacting of same with the platinum group metal- and tin-loaded porouscarrier material. A particularly preferred way of accomplishing thisrhenium carbonyl reaction step is an impregnation procedure wherein theplatinum group metal- and tin-loaded porous carrier material isimpregnated with a suitable solution containing the desired quantity ofthe rhenium carbonyl complex. For purposes of the present invention,organic solutions are preferred, although any suitable solution may beutilized as long as it does not interact with the rhenium carbonylcomplex and cause decomposition of same. Obviously, the organic solutionshould be anhydrous in order to avoid detrimental interaction of waterwith the rhenium carbonyl complex. Suitable solvents are any of thecommonly available organic solvents such as one of the available ethers,alcohols, ketones, aldehydes, paraffins, naphthenes and aromatichydrocarbons, for example, acetone, acetyl acetone, benzaldehyde,pentane, hexane, carbon tetrachloride, methyl isopropyl ketone, benzene,n-butylether, diethyl ether, ethylene glycol, methyl isobutyl ketone,diisobutylketone and the like organic solvents. Best results areordinarily obtained when the solvent is acetone; consequently, thepreferred impregnation solution is rhenium carbonyl complex dissolved inanhydrous acetone. The rhenium carbonyl complex suitable for use in thepresent invention may be either the pure rhenium carbonyl itself or asubstituted rhenium carbonyl such as the tin-containing complexes likeClSn[Re(CO)₅ ]₃ or the rhenium carbonyl halides including the chlorides,bromides, and iodides and the like substituted rhenium carbonylcomplexes. After impregnation of the carrier material with the rheniumcarbonyl component, it is important that the solvent be removed orevaporated from the catalyst prior to decomposition of the rheniumcarbonyl component by means of the hereinafter described pyrolysis step.The reason for removal of the solvent is that I believe that thepresence of organic materials such as hydrocarbons or derivatives ofhydrocarbons during the rhenium carbonyl pyrolysis step is highlydetrimental to the synergistic interaction associated with the presentinvention. This solvent is removed by subjecting the rhenium carbonylimpregnated carrier material to a temperature of about 100° F. to about250° F. in the presence of an inert gas or under a vacuum conditionuntil substantially no further solvent is observed to come off theimpregnated material. In the preferred case where acetone is used as theimpregnation solvent, this drying of the impregnated carrier materialtypically takes about one half hour at a temperature of about 225° F.under moderate vacuum conditions.

After the rhenium carbonyl component is incorporated into the platinumgroup metal- and tin (when the tin component is added prior to therhenium carbonyl incorporation step)-loaded porous carrier material, theresulting composite is, pursuant to the present invention, subjected topyrolysis conditions designed to decompose substantially all of therhenium carbonyl material, without oxidizing either the platnum group orthe decomposed rhenium carbonyl component. This step is preferablyconducted in an atmosphere which is substantially inert to the rheniumcarbonyl complex such as in a nitrogen or noble gas-containingatmosphere. Preferably, this pyrolysis step takes place in the presenceof a substantially pure and dry hydrogen stream. It is of course withinthe scope of the present invention to conduct the pyrolysis step undervacuum conditions. It is much preferred to conduct this step in thesubstantial absence of free oxygen and substances that could yield freeoxygen under the conditions selected. Likewise, it is clear that bestresults are obtained when this step is performed in the total absence ofwater and of hydrocarbons and other organic materials. I have obtainedbest results in pyrolyzing rhenium carbonyl while using an anhydroushydrogen stream at pyrolysis conditions including a temperature of about300° F. to about 900° F. or more, preferably about 400° F. to about 750°F., a gas hourly space velocity of about 250 to about 1500 hr.⁻¹ for aperiod of about 0.5 to about 5 or more hours until no further evolutionof carbon monoxide is noted. After the rhenium carbonyl component hasbeen pyrolyzed, it is a much preferred practice to maintain theresulting catalytic composite in an inert environment (i.e. a nitrogenor the like inert gas blanket) until the catalyst is loaded into areaction zone for use in the dehydrogenation of hydrocarbons.

The resulting pyrolyzed catalytic composite may, in some cases, bebeneficially subjected to a presulfiding step designed to incorporate inthe catalytic composite from about 0.01 to about 1 wt. % sulfurcalculated on an elemental basis. Preferably, this presulfidingtreatment takes place in the presence of hydrogen and a suitabledecomposable sulfur-containing compound such as hydrogen sulfide, lowermolecular weight mercaptans, organic sulfides, etc. Typically, thisprocedure comprises treating the pyrolyzed catalyst with a sulfiding gassuch as a mixture of hydrogen and hydrogen sulfide containing 1 to about10 moles of hydrogen per mole of hydrogen sulfide at conditionssufficient to effect the desired incorporation of sulfur, generallyincluding a temperature ranging from about 50° F. to about 1000° F. Itis generally a preferred practice to perform this presulfiding stepunder substantially water-free and oxygen-free conditions. It is withinthe scope of the present invention to maintain or achieve the sulfidedstate of the present catalyst during use in the dehydrogenation ofhydrocarbons by continuously or periodically adding a decomposablesulfur-containing compound, selected from the above-mentionedhereinbefore, to the reactor containing the superactive catalyst in anamount sufficient to provide about 1 to 500 wt. ppm, preferably about 1to about 20 wt. ppm. of sulfur, based on hydrocarbon charge. Accordingto another mode of operation, this sulfiding step may be accomplishedduring the pyrolysis step by utilizing a rhenium carbonyl reagent whichhas a sulfur-containing ligand or by adding H₂ S to the hydrogen streamwhich is preferably used therein.

According to the method of the present invention, the dehydrogenatablehydrocarbon is contacted with the attenuated superactive multimetaliccatalytic composite described above in a dehydrogenation zone maintainedat dehydrogenation conditions. This contacting may be accomplished byusing the catalyst in a fixed bed system, a moving bed system, afluidized bed system, or in a batch type operation; however, in view ofthe danger of attrition losses of the valuable catalyst and ofwell-known operational advantages, it is preferred to use a fixed bedsystem. In this system, the hydrocarbon feed stream is preheated by anysuitable heating means to the desired reaction temperature and thenpassed into a dehydrogenation zone containing a fixed bed of thecatalyst previously characterized. It is, of course, understood that thedehydrogenation zone may be one or more separate reactors with suitableheating means therebetween to insure that the desired conversiontemperature is maintained at the entrance to each reactor. It is also tobe noted that the reactants may be contacted with the catalyst bed ineither upward, downward, or radial flow fashion with the latter beingpreferred. In addition, it is to be noted that the reactants may be inthe liquid phase, a mixed liquid-vapor phase, or a vapor phase when theycontact the catalyst, with best results obtained in the vapor phase.

Although hydrogen is the preferred diluent for use in the subjectdehydrogenation method, in some cases other art-recognized diluents maybe advantageously utilized, either individually or in admixture withhydrogen or each other, such as steam, methane, ethane, carbon dioxide,and the like diluents. Hydrogen is preferred because it serves thedual-function of not only lowering the partial pressure of thedehyrogenatable hydrocarbon, but also of suppressing the formation ofhydrogen-deficient, carbonaceous deposits on the catalytic composite.Ordinarily, hydrogen is utilized in amounts sufficient to insure ahydrogen to hydrocarbon mole ratio of about 1:1 to about 20:1, with bestresults obtained in the range of about 1.5:1 to about 10:1. The hydrogenstream charged to the dehydrogenation zone will typically be recycledhydrogen obtained from the effluent stream from this zone after asuitable hydrogen separation step. As explained in my prior applicationSer. No. 68,278, now Pat. No. 4,256,566 a highly preferred mode ofoperation of the instant dehydrogenation method is in a substantiallywater-free environment; however, when utilizing hydrogen in the instantmethod, improved selectivity results are obtained under certain limitedcircumstances, if water or a water-producing substance (such as analcohol), ketone, ether, aldehyde, or the like oxygen-containingdecomposable organic compound) is added to the dehydrogenation zone inan amount calculated on the basis of equivalent water, corresponding toabout 1 to about 5,000 wt. ppm. of the hydrocarbon charge stock, withabout 1 to 1,000 wt. ppm. of water giving best results. This wateraddition feature may be used on a continuous or intermittent basis toregulate the activity and selectivity of the instant catalyst.

Regarding the conditions utilized in the method of the presentinvention, these are generally selected from the dehydrogenationconditions well-known to those skilled in the art for the particulardehydrogenatable hydrocarbon which is charged to the process. Morespecifically, suitable conversion temperatures are selected from therange of about 700° to about 1300° F. with a value being selected fromthe lower portion of this range for the more easily dehydrogenatedhydrocarbons such as the long chain normal paraffins and from the higherportion of this range for the more difficulty dehydrogenatedhydrocarbons such as propane, butane, and the like hydrocarbons. Forexample, for the dehydrogenation of C₆ to C₃₀ normal paraffins, bestresults are ordinarily obtained at a temperature of about 800° to about950° F.; on the other hand, for the dehydrogenation of propane, bestresults are usually achieved at a temperature of about 1150° F. to 1250°F. The pressure utilized is ordinarily selected at a value which is aslow as possible consistent with the maintenance of catalyst stabilityand is usually about 0.1 to about 10 atmospheres with best resultsordinarily obtained in the range of about 0.5 to about 3 atmospheres. Inaddition, a liquid hourly space velocity (calculated on the basis of thevolume amount, as a liquid, of hydrocarbon charged to thedehydrogenation zone per hour divided by the volume of the catalyst bedutilized) is selected from the range of about 1 to about 40 hr.⁻¹, withbest results for the dehydrogenation of long-chain normal paraffinstypically obtained at a relatively high space velocity of about 20 to 35hr.⁻¹ and for the more refractory paraffins at a space velocity of about3 to about 10 hr.⁻¹.

Regardless of the details concerning the operations of thedehydrogenation step, an effluent stream will be withdrawn therefrom.This effluent will usually contain unconverted dehydrogenatablehydrocarbons, hydrogen, and products of the dehydrogenation reaction.This stream is typically cooled and passed to a hydrogen-separating zonewherein a hydrogen-rich vapor phase is allowed to separate from thehydrocarbon-rich liquid phase. In general, it is usually desired torecover the unreacted dehydrogenatable hydrocarbon from thishydrocarbon-rich liquid phase in order to make the dehydrogenationprocess economically attractive. This recovery operation can beaccomplished in any suitable manner known to the art such as by passingthe hydrocarbon-rich liquid phase through a bed of suitable adsorbentmaterial which has the capability to selectively retain thedehydrogenated hydrocarbons contained therein or by contacting same witha solvent having a high selectivity for the dehydrogenated hydrocarbon,or by a suitable fractionation scheme where feasible. In the case wherethe dehydrogenated hydrocarbon is a mono-olefin, suitable adsorbentshaving this capability are activated silica gel, activated carbon,activated alumina, various types of specially prepared zeoliticcrystalline aluminosilicates, molecular sieves, and the like adsorbents.In another typical case, the dehydrogenated hydrocarbons can beseparated from the unconverted dehydrogenatable hydrocarbons byutilizing the inherent capability of the dehydrogenated hydrocarbons toeasily enter into several well-known chemical reactions such asalkylation, oligomerization, halogenation, sulfonation, hydration,oxidation, and the like reactions. Irrespective of how thedehydrogenated hydrocarbons are separated from the unreactedhydrocarbons, a stream containing the unreacted dehydrogenatablehydrocarbons will typically be recovered from this hydrocarbonseparation step and recycled to the dehydrogenation step. Likewise, thehydrogen phase present in the hydrogen-separating zone will be withdrawntherefrom, a portion of it vented from the system in order to remove thenet hydrogen make, and the remaining portion is typically recycledthrough suitable compressing means to the dehydrogenation step in orderto provide diluent hydrogen therefor.

In a preferred embodiment of the present invention wherein long chainnormal paraffin hydrocarbons are dehydrogenated to the correspondingnormal mono-olefins, a preferred mode of operation of this hydrocarbonrecovery step involves an alkylation reaction. In this mode, thehydrocarbon-rich liquid phase withdrawn from the hydrogen-separatingzone is combined with a stream containing an alkylatable aromatic andthe resulting mixture passed to an alkylation zone containing a suitablehighly acid catalyst such as an anhydrous solution of hydrogen fluoride.In the alkylation zone the mono-olefins react with alkylatable aromaticwhile the unconverted normal paraffins remain substantially unchanged.The effluent stream from the alkylation zone can then be easilyseparated, typically by means of a suitable fractionation system, toallow recovery of the unreacted normal paraffins. The resulting streamof uncoverted normal paraffins is then usually recycled to thedehydrogenation step of the present invention.

The following working examples are introduced to illustrate further thedehydrogenation method and the attenuated superactive multimetalliccatalytic composite of the present invention. These examples of specificembodiments of the present invention are intended to be illustrativerather than restrictive.

These examples are all performed in a laboratory scale dehydrogenationplant comprising a reactor, a hydrogen separating zone, heating means,cooling means, pumping means, compressing means, and the likecoventional equipment. In this plant, the feed stream containing thedehydrogenatable hydrocarbon is combined with a hydrogen-containing,substantially water-free, recycle gas stream and the resultant mixtureheated to the desired conversion temperature, which refers herein to thetemperature maintained at the inlet to the reactor. The heated mixtureis then passed into contact with the instant attenuated superactivemultimetallic catalyst which is maintained as a fixed bed of catalystparticles in the reactor. The pressures reported herein are recorded atthe outlet from the reactor. An effluent stream is withdrawn from thereactor, cooled, and passed into the hydrogen-separating zone wherein ahydrogen-containing gas phase separates from a hydrocarbon-rich liquidphase containing dehydrogenated hydrocarbons, unconverteddehydrogenatable hydrocarbons, and a minor amount of side products ofthe dehydrogenation reaction. A portion of the hydrogen-containing gasphase is recovered as excess recycle gas with the remaining portionbeing continuously recycled, after water addition as needed, throughsuitable compressing means to the heating zone as described above. Thehydrocarbon-rich liquid phase from the separating zone is withdrawntherefrom and subjected to analysis to determine conversion andselectivity for the desired dehydrogenated hydrocarbon as will beindicated in the Examples. Conversion numbers of the dehydrogenatablehydrocarbon reported herein are all calculated on the basis ofdisappearance of the dehydrogenatable hydrocarbon and are expressed inmole percent. Similarly, selectivity numbers are reported on the basisof moles of desired hydrocarbon produced per 100 moles ofdehydrogenatable hydrocarbon converted.

All of the catalysts utilized in these examples are prepared accordingto the following preferred method with suitable modification instoichiometry to achieve the compositions reported in each example.First, a tin-containing alumina carrier material comprising 1/16 inchspheres having an apparent bulk density of about 0.3 g/cc is preparedby: forming an aluminum hydroxy chloride sol by dissolving substantiallypure aluminum pellets in a hydrochloric acid solution, thoroughly mixingstannic chloride with the resulting sol in an amount sufficient toresult in a final catalyst containing the hereinafter specified amountsof tin, adding hexamethylenetetramine to the resulting tin-containingalumina oil, gelling the resulting solution by dropping it into an oilbath to form spherical particles of a tin-containing alumina hydrogel,aging, and washing the resulting particles with an ammoniacal solutionand finally drying, calcining, and steaming the aged and washedparticles to form spherical particles of a substantially halogen-free,tin-containing gamma-alumina containing substantially less than 0.1 wt.% combined chloride. Additional details as to its method of preparingthis alumina carrier material are given in the teachings of U.S. Pat.No. 2,620,314.

An aqueous impregnation solution containing chloroplatinic acid, nitricacid and (when an alkali or alkaline earth component is used) eitherlithium nitrate or potassium nitrate is then prepared. Thetin-containing alumina carrier material is thereafter admixed with theimpregnation solution. The amounts of the metallic reagents contained inthis impregnation solution are calculated to result in a final compositecontaining the hereinafter specified amounts of the metallic components.In order to insure uniform dispersion of the platinum componentthroughout the carrier material, the amount of nitric acid used in thisimpregnation solution is about 5 wt. % of the alumina particles. Thisimpregnation step is performed by adding the carrier material particlesto the impregnation mixture with constant agitation. In addition, thevolume of the solution is approximately the same as the bulk volume ofthe alumina carrier material particles so that all of the particles areimmersed in the impregnation solution. The impregnation mixture ismaintained in contact with the carrier material particles for a periodof about 1/2 to about 3 hours at a temperature of about 70° F.Thereafter, the temperature of the impregnation mixture is raised toabout 225° F. and the excess solution is evaporated in a period of about1 hour. The resulting dried impregnated particles are then subjected toan oxidation treatment in a dry air stream at a temperature of about975° F. and a GHSV of about 500 hr.⁻¹ for about 1/2 hour. This oxidationstep is designed to convert substantially all of the metallicingredients to the corresponding oxide forms. The resulting oxidizedspheres are subsequently contacted in a steam stripping step with an airstream containing about 1 to about 30% steam at a temperature of about800° to about 1000° F. for an additional period of about 1 to about 5hours in order to reduce any residual combined chloride to a value lessthan 0.5 wt. % and most preferably less than 0.2 wt. %. The oxidized andsteam-stripped spheres are thereafter subjected to a second oxidationstep with a dry air stream at 975° F. and a GHSV of 500 hr.⁻¹ for anadditional period of about 1/2 hour.

The resulting oxidized, stream-stripped carrier material particles arethen subjected to a dry reduction treatment designed to reducesubstantially all of the platinum component to the elemental state andto maintain a uniform dispersion of this component in the carriermaterial. This reduction step is accomplished by contacting theparticles with a hydrocarbon-free, dry hydrogen stream containing lessthan 5 vol. ppm. H₂ O at a temperature of about 1050° F., a pressureslightly above atmospheric, a flow rate of hydrogen through theparticles corresponding to a GHSV of about 400 hr.⁻¹ and for a period ofabout one hour.

Rhenium carbonyl complex, Re₂ (CO)₁₀, is thereafter dissolved in ananhydrous acetone solvent in order to prepare the rhenium carbonylsolution which is used as the vehicle for reacting rhenium carbonyl withthe carrier material containing the uniformly dispersed platinum andtin. The amount of the complex used is selected to result in a finishedcatalyst containing the hereinafter specified amount of carbonyl-derivedrhenium metal. The resulting rhenium carbonyl solution is then contactedunder appropriate impregnation conditions with the reduced,platinum-and-tin-containing alumina carrier material resulting from thepreviously described reduction step. The impregnation conditionsutilized are: a contact time of about one half to about three hours, atemperature of about 70° F. and a pressure of about atmospheric. It isimportant to note that this impregnation step is conducted under anitrogen blanket so that oxygen is excluded from the environment andalso this step was performed under anhydrous conditions. Thereafter, theacetone solvent is removed under flowing nitrogen at a temperature ofabout 175° F. for a period of about one hour. The resulting dry rheniumcarbonyl impregnated particles are then subjected to a pyrolysis stepdesigned to decompose the rhenium carbonyl component. This step involvessubjecting the carbonyl impregnated particles to a flowing hydrogenstream at a first temperature of about 230° F. for about one half hourat a GHSV of about 600 hr.⁻¹ and at atmospheric pressure. Thereafter, inthe second portion of the pyrolysis step, the temperature of theimpregnated particles is raised to about 575° F. for an additionalinterval of about one hour until the evolution of CO was no longerevident. The resulting catalyst is then maintained under a nitrogenblanket until it is loaded into the reactor in the subsequentlydescribed dehydrogenation test.

EXAMPLE I

The reactor is loaded with 100 cc of a catalyst containing, on anelemental basis, 0.375 wt. % platinum, 0.375 wt. % rhenium, 0.20 wt. %tin, and less than 0.15 wt. % chloride. This corresponds to an atomicratio of rhenium to platinum of 1.05:1 and of tin to platinum of 0.88:1.The feed stream utilized is commercial grade isobutane containing 99.7wt. % isobutane and 0.3 wt. % normal butane. The feed stream iscontacted with the catalyst at a temperature of 975° F., a pressure of10 psig., a liquid hourly space velocity of 4.0 hr.⁻¹, and a recycle gasto hydrocarbon mole ratio of 3:1. The dehydrogenation plant is lined-outat these conditions and a 20-hour test period commenced. The hydrocarbonproduct stream from the plant is continuously analyzed by GLC (gasliquid chromatography) and a high conversion of isobutane is observedwith a high selectivity for isobutylene.

EXAMPLE II

The catalyst contains, on an elemental basis, 0.375 wt. % platinum, 0.5wt. % rhenium, 0.25 wt. % tin, 0.6 wt. % lithium, and less than 0.15 wt.% combined chloride. These amounts correspond to the following atomicratios: Re/Pt of 1.4:1, Sn/Pt of 1.10:1, and Li/Pt of 45:1. The feedstream is commercial grade normal dodecane. The dehydrogenation reactoris operated at a temperature of 850° F., a pressure of 10 psig., aliquid hourly space velocity of 32 hr.⁻¹, and a recycle gas tohydrocarbon mole ratio of 5:1. After a line-out period, a 20-hour testperiod is performed during which the average conversion of the normaldodecane is maintained at a high level with a selectivity for normaldodecane of about 90%.

EXAMPLE III

The catalyst is the same as utilized in Example II. The feed stream isnormal tetradecane. The conditions utilized are a temperature of 830°F., a pressure of 20 psig., a liquid hourly space velocity of 32 hr.⁻¹,and a recycle gas to hydrocarbon mole ratio of 4:1. After a line-outperiod, a 20-hour test shows an average conversion of about 12%, and aselectivity for normal tetradecene of about 90%.

EXAMPLE IV

The catalyst contains, on an elemental basis, 0.2 wt. % platinum, 0.2wt. % rhenium, 0.1 wt. % and 0.4 wt. % lithium, with combined chloridebeing less than 0.2 wt. %. The pertinent atomic ratios are: Re/Pt of1.05:1, Sn/Pt of 0.82:1 and Li/Pt of 56:1. The feed stream issubstantially pure cyclohexane. The conditions utilized are atemperature of 900° F., a pressure of 100 psig., a liquid hourly spacevelocity of 3.0 hr.⁻¹, and a recycle gas to hydrocarbon mole ratio of4:1. After a line-out period, a 20-hour test is performed with almostcomplete conversion of cyclohexane to benzene and hydrogen.

EXAMPLE V

The catalyst is the same as in Example IV. The feed stream is commercialgrade ethylbenzene. The conditions utilized are a pressure of 15 psig.,a liquid hourly space velocity of 32 hr.⁻¹, a temperature of 1010° F.,and a recycle gas to hydrocarbon mole ratio of 3:1. During a 20-hourtest period, 85% or more of equilibrium conversion of the ethylbenzeneis observed. The selectivity for styrene is about 90%.

EXAMPLE VI

The catalyst contains, on an elemental basis, about 0.75 wt. % platinum,about 0.8 wt. % rhenium, 0.3 wt. % tin, about 0.6 wt. % lithium and lessthan 0.2 wt. % chlorine. The relevant atomic ratios are: Re/Pt of1.12:1, Sn/Pt of 0.66:1 and Li/Pt of 22.6:1. The charge stock issubstantially pure propane. The conditions utilized are: an inletreaction temperature of 1150° F., a pressure of 10 psig., a hydrogen topropane mole ratio of 2:1 and a liquid hourly space velocity of about 5hr.⁻¹. Results are: a conversion of propane of about 35% at aselectivity for propylene of about 85%.

It is intended to cover by the following claims all changes andmodifications of the above disclosure of the present invention whichwould be self-evident to a man of ordinary skill in thecatalyst-formulation art or in the hydrocarbon dehydrogenation art.

I claim as my invention:
 1. A nonacidic catalytic composite comprising a combination of a catalytically effective amount of a pyrolyzed rhenium carbonyl component with a porous carrier material containing a uniform dispersion of catalytically effective amounts of an alkali or alkaline earth component, a tin component and a platinum group component which is maintained in the elemental metallic state.
 2. A nonacidic catalytic composite as defined in claim 1 wherein the composite contains the components in amounts, calculated on an elemental basis, corresponding to about 0.01 to about 2 wt. % platinum group metal, about 0.01 to about 5 wt. % rhenium, about 0.005 to about 5 wt. % tin, and about 0.1 to about 5 wt. % alkali or alkaline earth metal.
 3. A nonacidic catalyst composite as defined in claim 1 wherein the porous carrier material is a refractory inorganic oxide.
 4. A nonacidic catalyst composite as defined in claim 3 wherein the refractory inorganic oxide is alumina.
 5. A nonacidic catalyst composite as defined in claim 1 wherein the platinum group component is platinum.
 6. A nonacidic catalyst composite as defined in claim 1 wherein the platinum group component is palladium.
 7. A nonacidic catalyst composite as defined in claim 1 wherein the platinum group component is rhodium.
 8. A nonacidic catalyst composite as defined in claim 1 wherein the platinum group component is iridium.
 9. A nonacidic catalyst composite as defined in claim 1 wherein the alkali or alkaline earth component is potassium.
 10. A nonacidic catalytic composite as defined in claim 1 wherein the alkali or alkaline earth component is lithium.
 11. A nonacidic catalyst composite as defined in claim 1 wherein the catalyst composite is in a substantially halogen-free state.
 12. A nonacidic catalyst composite as defined in claim 1 wherein the composite contains, on an elemental basis, about 0.05 to about 1 wt. % platinum group metal, about 0.05 to about 1 wt. % rhenium, about 0.01 to about 1 wt. % tin and about 0.25 to about 3.5 wt. % alkali metal or alkaline earth metal.
 13. A nonacidic catalytic composite as defined in claim 1 wherein the metals contents thereof is adjusted so that the atomic ratio of tin to platinum group metal is about 0.1:1 to about 13:1, the atomic ratio of alkali or alkaline earth metal to platinum group metal is about 10:1 to about 75:1 and the atomic ratio of rhenium, derived from the rhenium carbonyl component, to platinum group metal is about 0.2:1 to about 5:1. 